P816: PHARMACODYNAMIC ACTIVITY OF GEN3014 (HEXABODY-CD38) IN PATIENTS WITH MULTIPLE MYELOMA SUPPORTS ENHANCED COMPLEMENT DEPENDENT CYTOTOXICITY OF GEN3014 COMPARED TO DARATUMUMAB
Authors: Ida H. Hiemstra, Kim Santegoets, Maarten Janmaat, Wessel Ten Hagen, Rosanna Sanchez, Lauren Brady, Sieto Bosgra, Marije Overdijk, Jenny Chen, Katrine Fladeland Iversen, Torben Plesner, Esther Breij
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: CD38 monoclonal antibodies (mAb) have become part of backbone regimens for the treatment of multiple myeloma (MM). GEN3014 (HexaBody-CD38) is a next-generation CD38 mAb, carrying an E430G mutation in its Fc domain. This mutation facilitates IgG hexamer formation upon binding to CD38 on the cell membrane, leading to enhanced binding of complement and highly efficient complement-dependent cytotoxicity (CDC). In cell lines and primary MM patient samples, GEN3014 showed CDC-mediated tumor cell killing that was more efficient than daratumumab. In MM patients dosed with GEN3014, reduction in peripheral complement factor C2 and total complement lytic activity was observed at all evaluable doses (0.2-24 mg/kg). Complement parameters rapidly returned to baseline after dosing, indicating that GEN3014 did not exhaust complement (Spencer et al. ASH2022). Aims: To confirm the potent CDC activity of GEN3014, complement consumption was evaluated in GEN3014 or daratumumab treated samples in (A) preclinical studies under complement limiting conditions and (B) in patient samples from the current GEN3014 study vs. data previously reported from MMY2002. Methods: In vitro CDC assays were performed using variable concentrations of normal human serum (NHS), as a source of complement, and titrations with C2 under limiting complement conditions. Levels of complement factor C2 and complement lytic activity (CH50) were determined in the plasma or serum of patients dosed with GEN3014 during the dose escalation phase of the first-in-human, phase 1/2 trial of GEN3014 in patients with relapsed or refractory (RR)MM (NCT04824794). Results: At lower complement levels, maximal CDC-mediated tumor cell kill in vitro by GEN3014 and daratumumab was reduced, while the antibody concentration to reach the half maximal effect (EC50) was not affected. This indicates that a suboptimal CD38 mAb concentration does not augment the rate-limiting effect of complement. At all complement levels, GEN3014 showed higher CDC compared to daratumumab (Figure 1), indicating that GEN3014 more efficiently uses complement to induce tumor cell kill, also at lower complement levels. Adding C2 to low serum levels (partially) restored the CDC activity of GEN3014, indicating that C2 is a limiting factor for CDC under these conditions. In patients dosed with 8 or 16 mg/kg GEN3014, decreased complement factor C2 (mean peak change from baseline -51.0%, [range = 0 to -78.3%] n=11) and decreased complement lytic activity (CH50) (mean peak change from baseline -35.9% [range =0 to -91.6%] n=10) were observed. Peak decreases were observed within the first 48 hours after initial dosing with GEN3014. The observed decrease in C2 level for subjects treated with GEN3014 was more prominent than reported for daratumumab (mean 25% reduction from baseline at C1D2) (Nijhof et al 2016), which is in line with increased CDC activity of GEN3014 appreciated in vitro. Summary/Conclusion: GEN3014 showed potent CDC activity in vitro, with higher maximal kill compared to daratumumab, also under suboptimal complement conditions. GEN3014 induced a stronger decline of complement levels in patients compared to historical data of daratumumab, supporting its potential to induce enhanced CDC in patients. These findings support the ongoing phase 1/2 trial in patients with RRMM (NCT04824794) evaluating the safety and efficacy of GEN3014, which includes a head-to-head comparison with daratumumab.Figure 1 GEN3014 and daratumumab induced CDC under suboptimal complement conditions. CDC activity of GEN3014, daratumumab and an isotype control at a dose of 10 µg/mL and a dose range of normal human serum on SU-DHL-4 cells. The average percentage tumor cell kill from three independent experiment ± SD are shown. Keywords: CD38, Multiple myeloma, Complement